One type of laser which does not require end mirrors is the distributed feedback lasers described in U.S. Pat. No. 3,760,292 issued Sept. 18, 1973 to H. W. Kogelnik et al. In the distributed feedback laser the gain medium or the index of refraction is modulated at periodic intervals in order to provide reflections along the entire length of the gain medium. One form of distributed feedback laser that is proposed in the Kogelnik et al patent is a semiconductor laser in which a current mask is positioned within the laser structure in order to permit pumping or energizing current to pass through the active region of the laser only at periodic intervals along the length of the laser. Such a laser is shown in FIG. 5 of the Kogelnik et al patent. The net effect of the current mask is to produce a periodic gain variation within the semiconductor laser.
A new type of three terminal device was disclosed at the International Electron Devices Meeting in Washington, D.C., 1979 by scientists from the Massachusetts Institute of Technology, Lincoln Laboratory, Lexington, MA. This device is shown and described on page 130 of Electronics, Dec. 6, 1969. As shown in Electronics, the device is a permeable base transistor whose base consists of a layer of tungsten that has been patterned into a 3200 .ANG. period grating layer which layer is epitaxially embedded in a single crystal of n-type gallium arsenide. This transistor wherein the base is a grid-like metallic structure is said to provide many advantages over gallium arsenide field effect transistors.